Microwave radiation absorber comprising spaced parallel resistance discs



Oct. 6, 1964 E. B. M MILLAN MICROWAVE RADIATION ABSORBER COMPRISING SPACED PARALLEL RESISTANCE DISCS Filed Nov. 21, 1957 INVEN TOR.

United States Patent 3,152,328 MICROWAVE RADIATION ABSORBER COMPRIS- ING SACED PARALLEL SISTANCE DISCS Edward B. McMillan, Ipswich, Mass, assignor, by mesne assignments, to The McMillan Corporation of North Carolina, Raleigh, N.C., a corporation of North Carolina Filed Nov. 21, 1957, Ser. No. 697,901 1 Claim. (Cl. 343-18) The present invention relates to a wide range radiation absorber in sheet form which is operative in the microwave frequency range, and more particularly to an absorber of this type wherein the energy absorbing elements are spaced laminar sub-bodies in the form of resistance discs.

This application is a continuation-in-part of my copending application, Serial No. 292,089 filed June 6, 1952, now Patent No. 2,822,539 issued February 4, 1958.

The absorber of the present invention utilizes a series of stacked layers of impedance matching material to form the body of the absorber. Each layer of impedanec matching material has printed thereon discs of electrical energy absorbing material in the form of resistance discs. The edges of each group of sub-bodies cooperate with the edges of other sub-bodies within the group to define an envelope having sloped surfaces to divert reflected microwave energy away from the source of the energy.

The invention will be better understood from the following specification With reference to the accompanying drawing.

In the drawing, the single figure is a sectional view in elevation of an absorber embodying the invention, the energy which is to be absorbed entering the top or uppermost layer of the absorber.

Referring to the drawing, there is shown a compact microwave-radiation absorber, according to my invention, which was constructed in laminar form with electrical-energy-absorbing dielectric sub-bodies 53 printed on layers of an impedance-matching material 55 parallel to the outer surface. The absorber comprises thin, vertical, structural supports of wood such as shown at 57, relatively neutral in electrical action, to sustain mechanical loads bearing upon its front outer surface 59. Said resistance discs of electrical-energy-absorbing material 53 were printed with an adhesive paint comprising 50 weight parts of powdered iron from reduction of iron carbonyl, known as carbonyl iron, 50 weight parts of dry, uncured urea-formaldehyde resin containing a dry curing agent, and 40 weight parts of water. Said iron powder was found to be especially effective as an electrical-energy-absorbent conductive particle. The layers of impedance-matching material 55 were cemented together, with the edges of the resistance discs of electrical-energy-absorbing material 53 so arranged in diameter and superposition as to form a plurality of coneshaped absorbing bodies 61, 63, and 65. The electrical index of refraction of these absorbing bodies was substantially the average of the indices of the combined volumes of impedance-matching material 55 and electrical-energy-absorbing material 53 enclosed within said bodies, and had an effective value of 1.6. Incident microwave radiation 67 of wavelengths too great to permit propagation between sub-bodies 53 followed entrapping ray paths 69, 71, 73, and substantially as shown, while incident microwave radiation 77 of wavelengths short enough to permit propagation between sub-bodies 53 followed entrapping ray paths 79, 81, and 83, all of these ray paths leading to absorption of the energy of the radiation. The impedance-matching material 55 comprised a foam of natural rubber latex, having an electrical index of refraction of 1.1, and reduced the reflection from absorbing bodies 61, 63, and 65. The entire absorber was constructed so as to have a thickness of 4 /2, and the base of each absorbing body had a diameter 87 of 4". An absorption test before incident microwave radiation at 3.18 centimeters wavelength at 45, 60, and 70 degrees angles of incidence with respect to the normal gave power reflections 42, 39, and 34 decibels, respectively, below the incident power level for parallel and perpendicular polarizations of the wave with reference to the plane of incidence.

While I have shown and described what I believe to be the best embodiment of my invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claim.

What I claim is new and desire to secure by Letters Patent of the United States is as follows:

A microwave-radiation absorber comprising spaced laminar sub-bodies of electrical-energy-absorbing material, said sub-bodies being formed as resistance discs, at least one edge of each such sub-body of electricalenergy-absorbing material cooperating with corresponding respective edges of other spaced laminar sub-bodies to define an envelope having sloped surfaces to divert reflected microwave energy away from the source of said energy.

References Cited in the file of this patent UNITED STATES PATENTS 2,207,656 Cartwright et al July 9, 1940 2,293,839 Linder Aug. 25, 1942 2,331,716 Nadeau et al. Oct. 12, 1943 2,464,006 Tiley Mar. 8, 1949 2,474,384 Sunstein June 28, 1949 2,527,918 Collard Oct. 31, 1950 2,717,312 Taylor Sept. 6, 1955 2,724,112 Hepperle Nov. 13, 1955 2,828,484 Skellett Mar. 25, 1958 2,870,439 Stinehelfer J an. 20, 1959 2,977,591 Tanner Mar. 28, 1961 FOREIGN PATENTS 776,158 Great Britain June 5, 1957 OTHER REFERENCES Severin: IRE Transactions on Antennas & Propagation, July 1956, pp. 388-392. 

